Engine shake at idle

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chrisire

Cadet
Joined
Apr 21, 2012
Messages
10
1986 20 hp Evinrude, electric start tiller control on a 14 ft Sylvan Super Snapper. Engine fires right up every time runs great all the way through the power bands. Boat will just hit 22 mph with my wife and myself in the boat. My question is, at idle the engine shakes from side to side. Once you begin to give it throttle, it seems to smooth out. I have installed new plugs and then fired it up and let it run for 6-8 minutes on idle, then shut it down and pulled plugs to check that both cylinders are truly firing at idle. Yes, both cylinders are firing at idle. Any ideas as to what may be causing this?
 
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geoffwga1

Petty Officer 1st Class
Joined
Aug 8, 2010
Messages
394
Re: Engine shake at idle

At a guess I would say that the plugs are not firing at a true 180 Degrees from each other.This is much more noticeable at idle than at higher speeds.I don't know what the cure is on this late a model as it prolly doesn't have magneto ignition,I'm sure someone on here does though.
Geoff69a1
 
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chrisire

Cadet
Joined
Apr 21, 2012
Messages
10
Re: Engine shake at idle

Thanks for the reply Geoff69a1. As an added note, I am hitting 4930 RPM at WOT, out of a possible 5000 max. I replaced the CD2 power pack and both coils last winter and it made a huge difference in the overall running condition, but no change in the idle shake. Like I said, motor runs great. Would the condition you talk about just not appear at higher revs, or just not as noticible?
 
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boobie

Supreme Mariner
Joined
Nov 5, 2009
Messages
20,826
Re: Engine shake at idle

Have you done any carb work or tried to adjust the low speed mixture screw ??
 
K

kodibass

Master Chief Petty Officer
Joined
Apr 10, 2010
Messages
864
Re: Engine shake at idle

Check your upper motor mounts, there is one on each side just below the engine pan. they may be busted this will cause the motor to shake at idle.
 
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chrisire

Cadet
Joined
Apr 21, 2012
Messages
10
Re: Engine shake at idle

Carb was rebuilt last year. Problem was there b4 and after rebuild. As for the rubber engine mounts, I will check them out. Thanks for your help boobie and kodibass.
 
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